but many of the classes and subs called were not available. So I thought: no problem, I'll wrap a test framework around the code that provides a sub quux to return sample data and a sub AUTOLOAD to make sure things that need to return true.
Since some of the things that need to return true are constructors, I'll make it sub AUTOLOAD { bless {} }.

And I got it running; the real subs that existed got called; the sub quux that provided fake data got called; everything else was effectively a noop. But there was a problem with the output, and I needed to run it in the debugger, and ran into a mystery that stumped me for a little while. You can try it yourself; run perl -d -we'sub AUTOLOAD { bless {} } foo()' and note that "s" stepping into foo seems ineffective; you can do it over and over again without terminating. And using "n" gets you a "100 levels deep in subroutine calls!" warning.

In retrospect, the problem was simply solved by an additional sub declaration:

Although single stepping gives the 100 levels message, setting a breakpoint on AUTOLOAD catches the problem and gives you enough information about what is going on. I've encountered this one myself, when I was doing "creative" things with AUTOLOAD.

A more interesting and challenging problem is what happens when there is inheritance. Perl scans the @ISA tree and will call a sub there if it finds one. If there was no sub in the whole tree of name spaces, it then scans the @ISA tree for an AUTOLOAD sub. Have a peep inside the source code of my module Devel::Leak::Object for a convoluted example.

--

Oh Lord, won’t you burn me a Knoppix CD ?
My friends all rate Windows, I must disagree.
Your powers of persuasion will set them all free,
So oh Lord, won’t you burn me a Knoppix CD ? (Missquoting Janis Joplin)

Went to join the gridlock to see it
Held an eclipse party
Watched a live feed
I cn"t see tge kwubosd to amswr thus
I tried to see it, but 8000 miles of rock got in the way
What eclipse?
Wanted to see it, but they wouldn't reschedule it
Read the book instead